Process for recovering constituents of air or other gaseous mixtures



R. WUCHERER AND F. POLLITZER.

PROCESS FOR RECOVERING CONSTITUENTS OF AIR OR OTHER GASEOUS MIXTURES.

APPLICATION FlLED AUG.24. 1917.

Patented June 27, 1922.

lmz nl ll UNITED: srA'rEs PATENT orricn.

RunoLE wucnERER AND FRANZ roLLrrz R, or MUNICH, GERMANY, AssIGNoRs, BY MESNE ASSIGNMENTS, TO THE LINDE AIR rnonucrrs COMPANY, or NEW YORK,

N. Y., A CORPORATION OF OHIO.

PROCESS FOR REGOVERING CONSTITUENTS OF AIR OR OTHER GASEOUS MIXTURES.

Specification of Letters Patent. Patented June 27, 1922. I

Application filed August 24, 1917. Serial No. 188,039.

(GRANTED UNDER THE rnovrsroNs or THE ACT or MARCH 3, 1921, 41 STAT. I.., 1313.

To all whom it may concern:

Be it known that we, RUDoLF WUQHER R, a subject of the German Emperor, and FRANZ PoLLrrzER, a subject of the Emperor of Austria, both residing at Munich, Germany, have invented new and useful Improvements in Processes for Recovering Constituents of Air or Other Gaseous Mixtures, (for which we have filed an application in Germany in the name of Gesellschaft fur Lindes Eismaschinen A. G. Jan. 21, 1916), of which the following is a specification.

This invention relates to the recovery of constituents of gaseous mixtures, and particularly to the recovery of argon from these mixtures. In the following specification the invention is described, by way of example, in connection with air as a mixture to be separated. The process is applicable, however, to any other mixture of oxygen, nitrogen and argon, or to any other gas mixture having constituents the relative boiling points and mutual solubilities of which are similar to the corresponding properties of the constituents of air. 1

The term oxygen as used herein, therefore, comprehends generally not only oxygen but components of gas mixtures which have relatively high boiling points, while the term nitrogen as used herein includes not only nitrogen but other relatively low bolling components of gas mixtures.

In the separation of air for the purpose of obtaining argon, the air is first divided by liquefaction and rectification into two'fractions, one of which consists of more or less pure nitrogen and the OtlIBI Of which comprises more or less pure oxygen. This process as described, for example, in United States Patents Nos. 7 95,525, 815,544 or 815,- 601. consists in introducing liquid air into a rectifying column in which the liquid flows downward while the vapors formed from the liquid by supplying heat thereto rise in the column. The ascending vapors deprive the downflowing liquid of its nitrogen content and deliver oxygen to the liquid, which thus, on its way down the column, is enrlched in oxygen. By suitably controlling this process as described in our copendingapphcation Serial No. 879,492, the impure oxygen obtamed will contain a large proportion of the argon present in the air originally liquefied and this oxygen-argon mixture is introduced at a suitable point in a separate rectifying column for the purpose of obtaining from it a mixture still richer in argon.

In investigating the conditions upon which the efficacy of this latter rectification depends, 1t has been found that the quantity of heat whlch is transferred in the rectifying column is of deciding influence on the efiiciency of the process.

The process (like any other rectification process) requires a certain quantity of heat to be supplied at one point in the column, for example at or near the bottom, and the withdrawal of a certain quantity of heat at another portion of the column, for example at or near the top. If the mixture entering the column and the separate components leaving the column are all in liquid state, and at the same temperature, or if the proportion of gas and liquid and their temperatures are the same in the entering material as in the outgoing products, then 1 the amount of heat supplied to the column by means of a separate heating agent will be practically equal to the amount of heat abstracted from the column by the cooling agency employed at its top. If the proportion of gaseous material in the outgoing products is greater than in the material supplied to the column for treatment therein, it will be apparent that the heat supplied from outside sources must exceed that abstracted by the extraneous cooling agent by the amount which is required to gasify that portion of the material under treatment which entered the column as liquid and escaped in the gaseous condition. 4

We have discovered that a particularly efiicient rectification can be secured by so regulating the operation of the rectifying column that the amount of heat which is transferred between the extraneous heating and cooling agents is not substantially less than the amount of heat required for the evaporation of the entire amount of liquid in the mixtu e in oduce into the rectify- 100 ing column. In rectification processes as ordinarily carried out, a much smaller transfer of heat is employed.

It will be seen that the rectifying column represents one stage in two distinct heat circuits. A certain number of heat units are introduced into the rectifying column by rials will be approximately identical. This,

however, is not necessarily the case. The second heat circuit through the rectifying column includes the heating element wherein heat is supplied to the liquid under treatment by an extraneous heating agent, and the cooling element or condenser wherein heat is abstracted from gases formed in the rectifying column through the agency of an extraneous refrigerating substance. the heat contained in the incoming material under treatment is equal to that contained in the outgoing products of the separation, then the heat supplied from the extraneous heating agent must equal that abstracted from the column by the extraneous cooling agent in order to preserve the heat balance in the column.

As stated above, we find that,an advantageous result is obtained if the heat transferred through the column in what may be called the exterior heat circuit that is, from the exterior heating means to the exterior cooling means, is approximately equal to or greater than that which is required to evaporate all the material being fed into the column for treatment. It necessarily follows that if the mixture undergoing treatment is impure oxygen, compressed air at its liquefying point being employed as the heating agent and liquid nitrogen at its boiling point being employed as the extraneous cooling agent, and if the latent heats of evaporation of the impure oxygen, air and nitrogen are the same at the pressures to which they are respectively subjected, then air must be fed to the heating element at at least the same rate by weight as the impure oxygen is introduced into thecolumn, and the liquid nitrogen which is used to abstract heat from the column must of course be approximately equal in amount to the compressed air employed for heating.

The drawing illustrates diagrammatically a simple and convenient apparatus for performing our process.

The mixture referred to as impure oxygen, containing some nitrogen and a large proportion of the argon in the air originally treated, is delievered by a pipe 10 into a When rectifying column 11 having at its bottom a vessel 12 containing a heating coil 13. At the top of the column is a condenser 14 having a vapor outlet 15 and immersed in a refrigerant, preferably liquid nitrogen, in a vessel 16. The refrigerant is supplied through a pipe 17 and its vapors escape through an outlet pipe 18. A valved pipe 19 is provided to carry off the vapors, or vapors and liquid, or liquid alone from the vessel 12, according to the height of the liquid therein.

The liquid in vessel 12 is evaporated by the heating medium,-for example air under suitable pressure flowing through coil 13. A regulation of the amount of heat supplied to the column can be effected by the valves 20 and 21 which control the supply of impure oxygen to the column and the supply of compressed air to the coil 13; while the heat withdrawn can be regulated by the valves 22 and 23 which control the inflow of liquid nitrogen to the vessel 16 and the escape of the nitrogen vapors.

It will benoted that the quantity of heat abstracted from the column by the cooler need not be equal to the quantity of heat supplied by the heater, but may be either greater or less.

abstracted must come from the material passing through the apparatus; whereas if it is less than the heat supplied by the extraneous heating agent, the excess so supplied will be carried out in the separated products of rectification. Where we have spoken of the quantity of heat transferred from the heater to the cooler, this is not intended to mean that the entire quantity of heat must be added by the heater and also removed by the cooler. When either the quantity of heat added or the quantity abstracted at the cooler is approximately equal to or greater than the quantity of heat necessary to vaporize all the material fedto If it is greater than the quantity supplied, the additional heat units the rectifying apparatus, we are able to obsorbed by theevaporation of all the mixture being fed to the apparatus.

2. A process for obtaining by rectification from a mixture containing argon a fraction enriched in argon, which comprises, feeding the mixture to be treated to a rectification at which heat would be absorbed by the apparatus, and supplying heat to said apevaporation of all the mixture being fed to 15 paratus from an outside source at a rate not the apparatus.

materially less than that at which heat would be absorbed by the evaporation of all the mixture being fed to the apparatus.

3. A process for obtaining by rectification from a mixture containing argon a fraction enriched in argon, which comprises, feeding the mixture to be treated to a rectification apparatus, and abstracting heat from I said apparatus by an extraneous cooling agent at a rate not materially less than that y In testimony whereof, we have signed this specification in the presence of two subscribwitnesses. unich, this 30 day of June, 1917.

' R. WUCHERER.

DR. FRANZ POLLITZER.

Witnesses G. MONCH, P. EGGENDORFER. 

